1. Field of the Invention
The present invention relates to a radiographic imaging device. In particular, the present invention relates to a radiographic imaging device that includes sensors for radiation detection and that carries out detection of at least one of the start of irradiation of radiation, the end of irradiation of radiation, and the irradiated amount of radiation.
2. Description of the Related Art
Radiographic imaging devices using a radiation detecting element such as an FPD (flat panel detector), in which a radiation sensitive layer is disposed on a TFT (thin film transistor) active matrix substrate and that can convert radiation such as X-rays or the like directly into digital data, or the like, have been put into practice in recent years. As compared with a conventional imaging plate, an FPD has the advantages that an image can be confirmed immediately and video images as well can be confirmed, and the popularization of FPDs is advancing rapidly.
Various types of radiation detecting element have been proposed. For example, there is a direct-conversion-type radiation detecting element that converts radiation directly into charges at a semiconductor layer, and accumulates the charges. Moreover, there is an indirect-conversion-type radiation detecting element that once converts radiation into light at a scintillator of CsI:Tl, GOS (Gd2O2S:Tb), or the like, and, at a semiconductor layer, converts the converted light into charges, and accumulates the charges.
At the radiation detecting element, even in a state in which radiation is not being irradiated, charges are generated due to dark current or the like, and the charges are accumulated in the respective pixels. Therefore, during standby, the radiographic imaging device that uses the radiation detecting element repeatedly carries out a resetting operation of extracting and eliminating the charges accumulated in the respective pixels of the radiation detecting element. At the time of imaging, the radiographic imaging device stops the resetting operation, and, during the radiation irradiating time period, accumulates charges. After the irradiating time period ends, the radiographic imaging device carries out reading-out of the charges accumulated in the respective pixels of the radiation detecting element.
As a technique that synchronizes the timing of irradiating radiation and the timing of starting the accumulation of charges by the radiation detecting element, Japanese Patent Application Laid-Open (JP-A) No. 2002-181942 discloses a technique of placing a sensor for radiation detection individually outside of the imaging region of the radiation detecting element, and causing accumulation of the charges to be started by the radiation detecting element at the time when radiation is detected at this sensor for radiation detection.
There are cases in which noise arises at the radiation detecting element due to any of various external disturbances such as shock, temperature or the like at the respective lines that are laid. There are cases in which noise arises also in the line that is connected to the sensor for radiation detection such as that of JP-A No. 2002-181942.
Therefore, when, for example, the electric signal flowing through the line connected to the sensor for radiation detection is converted into digital data, and the value of the converted digital data is compared with a predetermined threshold value for radiation sensing, and, in accordance with whether or not the value of the digital data is greater than or equal to the threshold value, it is detected whether or not radiation is irradiated, the threshold value for radiation sensing must be made to be large in order to prevent erroneous sensing of the start of irradiation of the radiation due to noise that is superimposed on the lines. However, if the threshold value for radiation sensing is made to be large, the timing of detecting the start of irradiation of radiation may become late.